The international General Conference on Weights and Measures (CGPM) has approved a plan to redefine four of the seven base units of the International System of Units (SI) in terms of fixed values of natural constants. The initiative would make possible new worldwide levels of consistency and accuracy, as well as simplify and normalize the unit definitions.

Up until now, the system has been dependent on the prototype kilogram, an artifact adopted in 1889 and still used as the world’s physical standard for mass.

On Oct. 21, 2011, CGPM, the diplomatic body that has the authority under the Meter Convention to adopt such a sweeping change, approved a resolution declaring that the kilogram, the ampere, the kelvin, and the mole, “will be redefined in terms of invariants of nature; the new definitions will be based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively.”

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